(1) Field of the Invention
This invention relates to a method for the manufacture of a high-expansion type absorbent polymer. The polymer manufactured by the present invention is of a high-expansion type and enjoys a high permeability to gas. The gel which the polymer forms with absorbed water has no viscidity. Thus, the polymer is used as water-retaining materials for agricultural and horticultural soils and as sanitary materials (such as paper diaper and sanitary napkin).
(2) Description of the Prior Art
Absorbent polymers are advantageous synthetic polymers which are used as physiological articles, sanitary materials such as paper diaper, and water-retaining materials for agricultural and horticultural applications, which are also used in various applications such as solidification of sludge and dehydration of oils, and for which new uses are being developed. Concrete examples of such polymers which have been introduced to the art include (1) the hydrolyzate of a starch-acrylonitrile graft polymer (Japanese Patent Publication No. 46199/1978 and Japanese Patent Application Laid-open No. 4820/1980), (2) a modified cellulose (Japanese Patent Application Laid-open No. 80376/1975), (3) polysodium acrylate obtained by the reversed-phase suspension method (Japanese Patent Publication No. 30710/1979 and Japanese Patent Application Laid-open No. 26909/1981), (4) polysodium acrylate obtained by the aqueous solution polymerization method (adiabatic polymerization and thin-film polymerization) (Japanese Patent Application Laid-open No. 133413/1980), (5) a cross-linked water-soluble macromolecular substance (Japanese Patent Publication No. 23462/1968), and (6) a starch-sodium acrylate graft polymer (Japanese Patent Publication No. 46199/1978).
The methods for the manufacture of the absorbent polymers enumerated above, however, have entailed the following problems.
(1) Insufficient capacity for absorption of water or slow speed of absorption of water in spite of high capacity for water absorption. Or inferior dispersibility in water. PA0 (2) The gels which the absorbent polymers form with absorbed water are so viscid that the polymers, when used as sanitary materials, have the possibility of exerting adverse effects on the user's skin. PA0 (3) An aggregate which polymer particles form when they are swelled with absorbed water has poor permeability to gas. The polymer, when used as a water-retaining material for soil, therefore, has the possibility of rotting the roots in the soil.